Its odd you would have soft spots on the floor of an all fiberglass boat. There isn't any wood in the floor (or under the floor) on that boat. even the transom is 100% fiberglass. I would like to know what you find if you cut the floor out. thx
I ran a screw in about every 8", including the "L" shaped alum channel I attached above each of the openings where to brackets are welded to the toons (see pic)
I have the same brand / make pontoon and it was very annoying having to stop and clean this little"Skeg" every so often, so I cut it as shown below and I have not had any problem since.
